Valves for gas cylinder valves are now commonly equipped with a residual pressure device. The residual pressure is typically of the order of a few bars (for example 3 bars or 44 psi). This device prevents the penetration of impurities by potential reflux in the bottles in use, or by contact with the atmosphere in the bottles which are not connected and where the valve remains open.
This type of device usually consists of a calibrated check valve arranged upstream of a shut-off valve. This check valve is arranged so that resilient means exert a closing force, the valve being configured such that the high pressure inside the bottle readily pushes the valve to open when there is a flow rate demand. When stopping the flow, the valve closes, preventing reflux. When the bottle is nearly empty so that the pressure within it is lower than the setting pressure required to open the valve, no gas can be withdrawn. With the valve remaining permanently closed, the content of the bottle remains isolated from the outside even when the shut-off valve is open.
When filling the gas cylinder via the tap, the residual pressure device, by its construction, will naturally remain closed. It is therefore necessary to force it open to allow filling of the bottle.
Patent document U.S. Pat. No. 5,048,565 discloses a tap for a gas cylinder, provided with a closing valve, a residual pressure device and a safety valve. The residual pressure device can be actuated in the open position for filling via an opening device controlled pneumatically or mechanically (e.g. via a lever or external tool).
Patent document EP 0372279 A1 discloses a residual pressure device which can be brought into the open position by rotation of an actuating member according to a quarter turn. The valve and the actuating member are equipped with a cam device for converting the rotational movement of the actuating member into a translation movement of the valve.
The actuation for opening a residual pressure device as disclosed in the two above mentioned documents is in principle reserved for qualified personnel to fill bottles. It is indeed important that the device cannot be opened outside of the filling operations. The opening of the device requires a special procedure such as a connection to auxiliary compressed air or as the intervention of special tools.
Patent document U.S. Pat. No. 3,820,560 discloses a scuba bottle tap comprising a residual pressure device with a control lever. The latter is rotatable and acts on a shaft provided with cam profiles acting on a corresponding piece itself acting on the movable part of the residual pressure device. The actuating lever is used to force the device in its open position. It should be noted that the device has a movable seat which allows the filling of the bottle without opening the device with the lever. While the lever allows easy opening of the device, no security is provided to prevent opening of the device when the bottle is in use. The tap of this teaching is foreseen to provide a reserve supply of oxygen during diving. When the actuating lever is designed to give access to this reserve.
The technical problem to be solved by the invention is to provide a tap for a gas cylinder fitted with a residual pressure device and whose filling operation is facilitated.